Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $82.77   12.672%   $93.2586   $93.26   $93.25   $93.30  
  Purchase #2 $62.98   6.558%   $67.1102   $67.11   $67.10   $67.10  
  Purchase #3 $19.65   9.551%   $21.5268   $21.53   $21.55   $21.50  
  Purchase #4 $86.64   10.161%   $95.4435   $95.44   $95.45   $95.40  
  Purchase #5 $167.48   10.267%   $184.6752   $184.68   $184.70   $184.70  
  Purchase #6 $129.55   5.476%   $136.6442   $136.64   $136.65   $136.60  
  Purchase #7 $128.75   5.503%   $135.8351   $135.84   $135.85   $135.80  
  7 purchase totals = $677.82       $734.4936   $734.50   $734.55   $734.40